1. Field of the Invention
The present invention relates to a scroll compressor for compressing a gas to a high pressure or for use in a compression type refrigeration system such as a refrigerator, freezer, air conditioner or the like, and more particularly a means for pressing an orbiting scroll member against a stationary scroll member and a means for cooling the chamber of the scroll compressor.
2. Description of the Prior Art
In the refrigeration systems such as refrigerators, freezers, air conditioners and so on comprising a refrigerant compression means, a condenser, an expansion means and an evaporator, the scroll compressors are increasingly used as a compression means. Same is true for the compressors for compressing gases to high pressures.
In the scroll compressor, a stationary scroll member consisting of an end plate and an involute wrap and formed with a suction and discharge ports and an orbiting scroll member also consisting of an end plate and an involute wrap are internally meshed with each other. A rotation-preventive means or Oldham ring is interposed between the orbiting scroll member and the stationary scroll member or a casing means. The orbiting scroll member is drivingly connected to a drive shaft so that the orbiting scroll member is forced to make the orbiting motion relative to the stationary scroll member, whereby the spaces sealed between the stationary and orbiting scroll members are forced to reduce their volumes and consequently the gases in these spaces or compression chambers are forced to be compressed. A scroll compressor, an expansion device and a pump of the type described above are disclosed in detail in U.S. Pat. No. 3,884,599.
In the scroll type hydraulic equipment such as a scroll compressor, an expansion device or a pump, as the gas trapped in the spaces between the stationary and orbiting scroll members is forced to flow toward the axis of rotation thereof, the pressure of the gas is gradually increased. As a result, the raised or increased pressure tend to separate the stationary and orbiting scroll members from each other. When they are separated from each other in the axial direction, the gas entrapped between them escapes through an annular space between them so that the compression efficiency considerably drops.
There have been proposed various schemes for preventing the axial separation between the stationary and orbiting scroll members, thereby maintaining the secure axial sealing therebetween. For instance, according to U.S. Pat. No. 2,881,089, spring means are interposed between the orbiting scroll member and a casing so as to press the orbiting scroll member against the stationary scroll member. U.S. Pat. No. 3,600,114 proposes that the discharged or compressed gas is forced to flow into the space behind the orbiting scroll member, thereby pressing the latter against the stationary scroll member. According to the commonly assigned co-pending U.S. application, Ser. No. 887,252, now abandoned, the compressed gas is bypassed into the interior of a casing from the intermediate compression chambers so that the orbiting scroll member is pressed against the stationary scroll member under the force of this partially compressed gas. In addition, the commonly assigned co-pending U.S. application, Ser. No. 967,893 discloses that the partially compressed gas is forced to flow from the intermediate compression chambers into a chamber or space surrounding a motor and a compressor, thereby not only pressing the orbiting scroll member against the stationary scroll member but also cooling the component parts enclosed in the casing.
According to the above-cited U.S. Pat. Nos. 2,881,089, 3,600,114 and 3,884,599, the satisfactory axial sealing between the stationary and orbiting scroll members can be maintained, but they do not propose any means for reducing the frictional losses between them. More specifically, when the springs are interposed between a rotating or moving member (that is, the orbiting scroll member) and a stationary member (that is, the casing), the area of contact between them is inevitably increased and consequently the frictional losses increase. Furthermore, the contact pressure provided by the springs is constant and the coefficient of static friction is greater than the coefficient of rolling friction. In addition, when the scroll compressor is started, the pressure of the gas entrapped between the stationary and orbiting scroll members is low. As a result, there exists a greater difference between the separating force and the pressing force, resulting in an excessive net pressing force. Consequently, the frictional force between the stationary and orbiting scroll members becomes too great to start the scroll compressor.
In the system wherein the partially compressed gas is used to press the orbiting scroll member against the stationary scroll member, the pressure receiving surface area must be restricted so that the pressing and separating forces may be maintained in desired equilibrium. As a result, the construction becomes very complicated.
According to the systems disclosed for instance in the above-recited U.S. applications, Ser. Nos. 887,252 and 967,893, the pressing force of a suitable degree of magnitude can be maintained without causing any adverse effects, but they do not propose any means adequate for sufficiently cooling the component parts enclosed in the casing or the like. As described above, according to U.S. application, Ser. No. 967,893, the gas is forced to flow into the chamber surrounding the motor so that the latter may be cooled. However, the pressure differential between an inlet and an outlet of the chamber is small so that the flow rate of the gas passing through the chamber is low and, consequently, the satisfactory cooling of the motor cannot be attained. It might be suggested to increase the aforementioned pressure differential, but the result would be that, although the flow rate could be increased, the pressure in the chamber would be disturbed and, consequently, the pressing force become nonuniform.